The present invention relates to an electrophotographic type image forming device used in laser printers, photocopiers, facsimile machines, and the like.
A conventional electrophotographic type image forming device, such as a laser printer, has been disclosed, for example, in laid open Japanese patent application publication No. HEI-10-35941. In this type of image forming device, a toner image formed on a photosensitive drum is transferred to a sheet or another recording medium as the medium passes between a transfer roller and the photosensitive drum. Subsequently, the recording medium passes between a single heat roller and a single pressure roller, causing the toner to melt by heat and fixing the toner image to the surface of the recording medium. A sheet supply unit is provided for supplying the recording medium stacked in a sheet supply tray, one sheet at a time. The sheet of the recording medium is conveyed from the sheet supply unit to an image forming section at which the photosensitive drum opposes the transfer roller through a conveying path by a sheet supply roller, a plurality of intermediate conveying rollers, and a register roller provided along the conveying path. The register roller is intermittently driven while the plurality of intermediate conveying rollers are rotated. A leading edge of the image recording medium abuts against the stopped register roller while the medium is fed by the conveying rollers, so that an intermediate area of the recording medium can be flexed. As a result, the leading edge can be aligned with a proper orientation, while the supply timing of the medium to the image forming section can be adjusted.
When forming images on a plurality of recording mediums in succession, the start timing for supplying the second and subsequent sheets from the sheet supply unit is set as follows. If the trailing edge of the preceding sheet is too close to the leading edge of the following sheet, a leading edge of a subsequent sheet may reach a sheet sensor disposed along the conveying path from the sheet supply unit to a discharging unit prior to the detection of completion of passing of the precedent sheet through the sheet sensor due to unevenness of leading edge positions of the sheets in the sheet supply tray. In the latter case, judgment is made such that the precedent sheet is not subject to feeding but staying at the sheet sensor position, and accordingly, an error processing attendant to sheet jamming is improperly executed.
If the subsequent sheet is fed prior to the separation of the trailing edge of the precedent sheet from the sheet supply roller, unwanted force is applied to the precedent sheet, which degrades sheet conveying performance. To avoid this problem, normally, the start timing for supplying sheets is set such that an interval of a prescribed amount, for example approximately 60 mm, is provided between the trailing edge of the preceding sheet and the leading edge of the following sheet taking also image data developing period into consideration.
For supplying each one sheet from the sheet supply unit, a frictional separating mechanism is used for separating the one sheet from the remaining sheet stack. One such frictional separating mechanism employs a separation pad pressing against the sheet supply roller to generate friction for separating the sheets. However, sometimes the leading edges of the sheets in the sheet supply unit become uneven, when using such frictional separating mechanism, a following sheet can oppose the frictional force between the sheet supply roller and frictional separating pad and move in the conveying direction as the preceding sheet is conveyed due to attractive force between the preceding uppermost sheet and the subsequent lower sheet stacked in the sheet supply tray. In this case, the subsequent sheet stops with its leading edge shifted downstream in the conveying direction from a reference position at the nip area between the sheet supply roller and frictional separating pad when the sheet supply roller has stopped.
If the following sheet stops with its leading edge shifted too far downstream from the reference point at the nip area when the sheet supply roller stops, the required condition of maintaining a prescribed interval between neighboring sheets cannot be met. Hence, when the sheet supply roller is driven to rotate at a prescribed timing designed to maintain a prescribed interval between sheets, it is possible that the sheet sensors will detect a sheet jam or that sufficient time is not allocated for developing the image data to be printed.
The present invention provides an image forming device for forming an image on a cut image recording medium including a drive source, a sheet feeder unit, an image forming unit, a conveying path, and at least two sheet conveying units. The sheet feeder unit stores therein a stack of image recording mediums. At the image forming unit a visible image is formed on the image recording medium. The conveying path extends between the sheet feeder unit and the image forming unit. Each image recording medium is conveyed through the conveying path in a conveying direction from the sheet feeder unit to the image forming unit. The at least two sheet conveying units are connected to the drive source and include a downstream side conveying unit and an upstream side conveying unit. The downstream side conveying unit is disposed along the conveying path for conveying the image recording medium at a first conveying speed. The upstream side conveying unit is disposed along the conveying path and an upstream of the downstream side conveying unit in the conveying direction for conveying the image recording medium at a second conveying speed higher than the first conveying speed.
In one embodiment, the image forming device further includes at least two clutches including a first clutch and a second clutch, and a controller. The first clutch is connected between the drive source and the downstream side sheet conveying unit and provides a power connection state for driving the downstream side conveying unit and a power disconnection state for shutting off power transmission to the downstream side conveying unit. The second clutch is connected between the drive source and the upstream side sheet conveying unit and provides a power connection state for driving the upstream side conveying unit and a power disconnection state for shutting off power transmission to the upstream side conveying unit. The controller controls the at least two clutches so as to provide the disconnection state in the upstream side conveying unit when the downstream side sheet conveying unit holds a leading edge portion of the image recording medium.
In another aspect of the invention, there is provided an image forming device for forming an image on a cut image recording medium including a drive source providing a driving force, a sheet feeder, an image forming unit, a conveying path, a first sheet conveying roller, a first clutch, second clutch, and a controller. The sheet feeder unit includes a sheet storing portion in which a plurality of image recording mediums are stacked in a sheet stack. The sheet supply roller is adapted for separating one image recording medium from a remaining sheet stack and for feeding the separated image recording medium in a sheet feeding direction. At the image forming unit a visible image is formed on the image recording medium. The image forming unit includes a photosensitive member carrying an electrostatic latent image where developing agents are carried as a developing agent image, and a transfer roller for transferring the developing agent image onto the image recording medium. The conveying path extends between the sheet feeder unit and the image forming unit. Each image recording medium is conveyed through the conveying path in the sheet feeding direction from the sheet feeder unit to the image forming unit. The first sheet conveying roller is disposed along the conveying path and between the sheet supply roller and the transfer roller. The first sheet conveying roller provides a peripheral speed lower than that of the sheet supply roller and higher than that of the transfer roller. The first clutch is connected to the first sheet conveying roller for selectively transmitting the driving force of the power source to the first sheet conveying roller. The first clutch provides power connection phase for driving the first sheet conveying roller and provides a power disconnection phase for stopping the first sheet conveying roller. The second clutch is connected to the sheet supply roller for selectively transmitting the driving force of the power source to the sheet supply roller. The controller includes shut-off means, and drive start means. The shut-off means provides the power disconnection phase after a trailing edge of a precedent image recording medium is moved past the first sheet conveying roller, so that a leading edge of a subsequent image recording medium abuts the stopped first sheet conveying roller for regulating an interval between the trailing edge of the precedent sheet and the leading edge of the subsequent sheet. The drive start means provides the power connection phase of the first clutch for starting driving rotation of the first sheet conveying roller after the regulation of the interval.
In still another aspect of the invention, there is provided an image forming device for forming an image on a cut image recording medium including a sheet feeder unit, an image forming unit, a conveying path and a sheet leading edge position regulating unit. The sheet feeder unit stores therein a stack of image recording mediums, and includes a separation unit that intermittently separates one sheet of the stack from a remaining stack at a separating position and feeds the one sheet in a sheet feeding direction. At the image forming unit a visible image is formed on the image recording medium fed from the sheet feeder. The conveying path extends between the sheet feeder unit and the image forming unit. Each image recording medium is conveyed through the conveying path in the sheet feeding direction from the sheet feeder unit to the image forming unit. The sheet leading edge position regulating unit has a part selectively protrudable, near the separating position, into the sheet conveying path to provide a protruding position and selectively retractable away from the sheet conveying path to provide a retracting position. A leading edge position of the image recording medium is regulated upon protrusion of the part into the sheet conveying path.